Method of treating metals



Patented Aug; 15, 1933 UNITED STATES v 1,923,058 METHOD OF TREATINGMETALS Harry Raymond Lowstuter, Monessen, Pa.

No Drawing. Application August 19, 1930 Serial No. 476,453

3 Claims. (01. 205-21) The present invention, relating as indicated to amethod of treating metals, is more particularly directed to a method oftreatment of such metals as steel, for example, for the purpose ofconditioning and protecting the same during working to partially orwholly prevent hardening of the metal during working operations, whetherthe operations be that of drawing, rolling, forging, or any otheroperation, producing a flow of the metal and a change in form of thearticle in question. A further object of the invention is the provisionof a method for integrally aflixing a coating of a protective nature tothe exposed surface of an article of the material referred to. A stillfurther object is the provision of a bimetallic product in the form of abase of such metal as steel, for example, coated with a relatively thinprotectivecoating of a material such as aluminum in which two metals areintegrally bonded together.

The principal object of the invention is the provision of a method ofcoating the metal to be worked with a material which apparently alloyswith the surface of the metal article, or at least so firmly adheresthereto that it is not removed by ordinary working operations, and whichhas the effect of apparently insulating the article from the usualeffects of the flowing of metal, that is, from the effect of the metalshardening in proportion to the amount of plastic deformation under therolling, forging or other treatment.

To the accomplishment of the foregoing and related ends, said invention,then, consists of the means hereinafter fully described and particularlypointed out in the claims; the following description setting forth indetail one approved method of carrying out the invention, such disclosedmethod, however, constituting but, one of the various ways in which theprinciple of the invention may be used.

My invention consists, briefly stated, in. treating the metal articlewhich is to be worked with a mixture of finely divided metal capable ofalloying or adhering firmly thereto and an acid or salt having fluxingproperties. The article when so coated or treated with this mixture,which may be suspended for convenience in a suitable vehicle, such forexample as water, varnish or similar material, is then furnaced to driveoil. the flux, leaving the metal of the composition coating firmlyunited to the surface of the article which is to be worked.

As an example of the composition which I hav found successful for thepurpose indicated, I have used'a mixture consisting of equal parts offinely divided aluminum and finely divided boric acid. This mixture isthen suspended either in a resin varnish, water or other non-carbonizingmaterial in the proportions of from 20 to 25 parts of the mixture to 15to 80 parts of the varnish. Y

The metal to be coated, for example steel, is first cleaned by beingpassed through an acid bath, after which it is ixmnediately dipped intomy improved mixture which forms a coating all over the metal article andis then heated to approximately 1450-1475 Fahn, or such temperature aswill insure the thorough bonding of the two metals employed. In thisoperation the liquid, of course, has been entirely evaporated or burnedoff, leaving a coating which appears to contain aluminum and which isfirmly bonded to, or alloyed with the surface of the metal article. Itis important that the steel or other metal to be coated be in anabsolutely clean condition for coating, and to insure this the materialshould be dipped into the coating bath immediately following thecleaning bath. It is also im portant that the coated material be heatedimmediately following the dipping as any delay al lows the coatingmaterial, and particularly the vehicle if varnish is employed, toharden.

Other materials may be employed for the suspending vehicle instead ofvarnish -or water, and I have used a starch base of about the usualconsistency with good results, while still other materials, such as gumsand compositions low in carbon can'also 'beemployed.

I am unable to explain the action which occurs from the use of myimproved coating, further than to say that there is apparently an interaction between the coating metal, that is the aluminum, and the basemetal, such for example a steel, produced by the boric acid andthetemperature at which the coated article is heated. The aluminum,however, is coated integrally onto the steel and forms a continuouscoating over the entire surface which remains throughout the drawing orother forming operations and which becomes smoother and more highlypolished with each succeeding operation affecting the article Theresulting product is therefore an article having a relatively thin butcontinuous coating containing or formed of a light non-rusting material,such as aluminum. Tests indicate that the mixture of aluminum and boricacid when fused together onto the metal in the manner indicated producesan alloy at the surface or at the point of junction between the coatingand the article consisting of an iron aluminum boride, although there-isalso probably free aluminum contained 11 in the coating and eithermechanically bonded thereto or bonded directly to the surface of themetal article.

In the drawing of tubes employing my improved process the tube is firstcoated as already described, then furnaced to fix and bond the aluminumcoating on the steel, after which a lubricating composition is appliedto the surface of the coated tube in the usual practice. Thereafter, atleast for a number of draws or passes, no further lubricatingcomposition need be applied. As the metal is protected from the effectsof hardening during these operations it does not require to be pickledor annealed and hence the original lubricating composition remains onthe surface and serves for all of the operations required without theapplication of any successive lubricating coatings. I

I am unable to accurately describe the action which occurs by reason ofthe presence of the coating described. The steel or other metal which isbeing worked does harden under the action of the working, but does notbecome sufficiently brittle to break, although it hardens progressivelywith repeated cold working. The action of the coating is, I think,partially a lubricating action which prevents the usual effect of theworking tools on the surface of the article undergoing the working. Forexample, if a tube is being drawn the die through which it passesordinarily exerts a tremendous pull on the surface of the tube causing ahardening of the metal and eventually the formation of very slightcracks in the surface of the material which, upon further working, causeimmediate breakage transversely of the article. The action of thecoating apparently is to partially lubricate the surface of the article,reducing the frictional drag or action of the dies in the case of drawnarticles and preventing or putting off the formation of hair-line crackswhich eventually lead to breakage. It is also possible that the coatingexerts an insulating effect and causes the material to retain withinitself the heat generated by the molecular arrangement during the draw,thus permitting the heat thus generated to partially, at least,self-anneal the tube or other article. It will be understood, however,that I put forward these theories purely as suggestions and that I donot state them as accurate conclusions.

In the drawing of tubes in which both the outer and inner surfaces areaffected the tube is of course coated with my composition both insideand out, and thus both surfaces are protected and covered with the thincoating of the non-rusting or light metal.

The uses to which the present invention may be put are obviously verynumerous and will suggest themselves readily to those skilled in thevarious arts, but among the uses may be mentioned protection to metalsfor all sorts of forming or flowing operations such as rolling, forging,drawing, hammering and the like. The primary effect of this treatment ofmetal is to prevent entirely, or at least to greatly reduce, the effectof flowing of the metal in various operations. Tubes coated by myimproved method can be subjected to a number of passes, greatly changingthe diameter and wall thickness of the tube, without hardening of themetal to an extent causing breakage and without any intermediatepickling or annealing operations. I have drawn tubes 8.

varying number of passes without any intermediate annealing and evenwithout relubrication of the surface of the material. For example, Ihave drawn a series of tubes, giving the initial tube seven successfuldraws, reducing the diameter and wall thickness at each draw, and havethen further reduced the tube thus produced by five sinking operationswithout any intermediate pickling or annealing, and 'without anyrelubrication except a single thin coating of lubricant between thedrawing and the sinking operations. By a sinking operation I mean adrawing operation in which the tube diameter is reduced, but withoutreduction in the wall thickness. I have drawn tubes through from four totwelve passes without a single intermediate annealing and have found themetal in the final article of substantially the same hardness as in theoriginal tube. This action I am unable to explain, but I havesatisfactorily demonstrated it on many 00- casions and with differenttypes of materials, when the operations to which the articles weresubjected were drawing, rolling, forging and hammering operations.

Other modes of applying the principle of my invention may be employedinstead of the one explained, change being made as regards the methodherein disclosed, provided the step or steps stated by any of thefollowing claims or the equivalent of such stated step or steps beemployed.

I therefore particularly point out and distinctly claim as myinvention:-

1. In a method of drawing tubes, the steps which consist in applying tothe inner and outer surfaces of the tube, a varnish low in carbon havingfinely powdered aluminum suspended therein, fixing and bonding suchfinely divided aluminum on to the surface of said tube in the form of athin continuous film, and then drawing said tube through successive diesto modify its diameter or thickness without intermediate heatingoperations. a

2. In a method of drawing tubes, the steps which consist in applying tothe inner and outer surfaces of the tube, a varnish low in carbon havingfinely powdered aluminum suspended there in, fixing and bonding suchfinely divided aluminum on to the surface of said tube in the form of athin continuous film, applying a coating of lubricating composition tothe surface of said tube, drawing said tube through dies to modify itsdiameter, and thenrecoating said tube with lubricating composition, andre-drawing it a number of times to further modify its diameter orthickness without intermediate annealing operations.

3. In a method of treating steel to prevent hardening during operationsinvolving flowing of the metal, the steps which consist in applying tothe surface of the steel, a liquid low in carbon Y

